A nitride semiconductor device 1 includes a first nitride semiconductor layer 4, constituting an electron transit layer, a second nitride semiconductor layer 5, formed on the first nitride semiconductor layer 4 and constituting an electron supply layer, a nitride semiconductor gate layer 6, disposed on the second nitride semiconductor layer 5 and containing an acceptor type impurity, a metal film 7, formed on the nitride semiconductor gate layer 6, and a gate pad 23, connected to the metal film 7 via a gate insulating film 8 having a first surface and a second surface, the first surface of the gate insulating film 8 is electrically connected directly or via a metal to the metal film 7, and the second surface of the gate insulating film 8 is electrically connected directly or via a metal to the gate pad 23.